In a letter to Verizon, Senators on the Commerce Committee challenged the company's practice of placing a "super cookie" oncustomers' smartphones. The letter follows the recent discovery that the advertising company Turn was secretly tracking Verizon customers, even after customers deleted its cookies. In the letter, the Senators asked Verizon to stop tracking users with undeletable cookies. EPIC has urged the White House and the Federal Trade Commission to limit the use of persistent identifiers. EPIC supports opt-in requirements and Privacy Enhancing Techniques for consumers, and algorithmic transparency for data collectors.